Cutting 6mm aluminum plate

J

JC99

Well-known member
I want to cut into my skid plate to enlarge a cut out that currently partly covers one oil screen bolt, everything else is accessible with the plate on for an oil change. Taking the skid plate off to remove this one bolt is getting tiresome as it’s fiddly with multiple screws/bolts etc. This is a reasonably common mod but I want to make sure I do it right and the actual method hasn’t been posted anywhere I could find, just the enlarged access hole shape. I have drills/dremels/orbital tool and angle grinder etc and I want to do this job with the plate on the bike preferably (seriously, it’s a pain in the ass to remove).

What’s the best way to do this in 6mm aluminum plate? My current thoughts are to use a drill to drill holes marking the corners/edges of the shape I want (I bought a 1/4” hardened metal bit today just in case) then a metal cutting blade on the orbital tool to connect the drill holes and finally a grinding bit on the dremel to smooth the edges. I think the extra cut I need to make is only about 1” by 1” but maybe a bit more.

Would that work? Would it be better to just use a cut off disc on the Dremel for everything? I don’t think the angle grinder would work for smaller length cuts etc.
 
Do you have enough room under the bike to even use a drill? How much clearance between the skid plate and the expensive stuff behind it? If you don't want to dismount the plate you might want to grab your wife's best cutting board and jam it behind the plate just in case.

I haven't had great luck with cutoff wheels or grinding bits on aluminum, but maybe that's just the ones I was using. They clogged up fast with the soft aluminum. I'd consider a hole saw for a nice clean shape, but a coping saw and file would work just as well if you resign yourself to dismounting and remounting the plate one last time.
 
Aluminium and grinding media usually don't play nice. It clogs up the grinding media and stops grinding in no time flat.

IMO drill a small hole aligned with where you want the clearance hole, then take the part off the bike and complete the job with a hole saw. Any reasonable method of making a "nice" hole is going to need clearance behind the part for the tool (e.g. saw blade, drill bit, file, etc) to do its job. It will be easier and less risky to do this with the part being cut, removed from the bike so as to not put expensive bike parts at risk.
 
Hmmm. Thanks for the advice about grinding wheels etc.

I have room to manoeuvre a drill as the hole enlargement I need to make is at the side of the skid plate, not underneath. Between the plate and any bike bits there’s a decent amount of space too so I'm not overly concerned that I'd do any damage with a drill. There’s enough space between the plate and bike parts at this enlargement point that I can actually get some to and fro movement with a saw blade too so I was thinking a jewellers saw might even work.

Taking the part off might be the easiest approach, this one last time though.
 
If you have a jigsaw and tons of room to work, you could shorten a jigsaw blade (grind it down on a belt/disc sander) so that it isn't long enough to contact the bike bits behind the plate. I'd still want to remove the plate to clean up the edges of the cut with a file, though.
 
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